Quantification of tributaries contributions using a confluence-based sediment fingerprinting approach in the Canche river watershed (France)

(IF 5.59 [2018]; Q1)International audienceSince a few years, land use management aims to reduce and control water erosion processes in watersheds butthere is a lack of quantitative information on the contribution of the sources of transported sediment. This ismost important in agricultural areaswhere soils are sensitive to erosion. The geology of these areas is often characterizedby large expanses of relatively homogeneous quaternary silts. The possibility of distinguishing thesources of erosion according to their geological substratum is thus very delicate. This information is importantbecause its lack can lead to the mis-implementation of erosion control measures. To address this request, aconfluence-based sediment fingerprinting approach was developed on the Canche river watershed (1274 km2;northern France), located in the European loess belt, an area that is affected by diffuse and concentrate erosionprocesses. Suspended particulate matter was collected during five seasonal sampling campaigns using sedimenttraps at the outlet of each tributary and confluencewith the main stream of the Canche river. The final compositefingerprintwas defined using physico-chemical and statistical analyses. The best tracer parameters for each tributarywere selected using stepwise discriminant function analyses. These parameters were introduced into amass balance mixing model incorporating Monte-Carlo simulations to represent the uncertainty. Estimates ofthe overall mean contributions fromeach tributary were quantified at different temporal scales. The annual sedimentflux tributaries contributions range from 3 to 22% at the outlet of the Canche river, and annual sedimentflux range from 0.87 to 40.7 kt yr−1. The Planquette and the Créquoise tributaries appear to be those producing the largest sediment flux. In contrast, tributarieswith the highest number of erosion control on their area exhibitthe lowest values of sediment flux. Our results indicate a positive impact of recent land management policies inthe Canche river watershed